Switch of the circuit breaker type



March 15, 1966 J. SOHNS 3,240,996

SWITCH OF THE cmcum BREAKER TYPE Filed Feb. 18, 1965 United StatesPatent 3,240,996 SWITCH OF THE CIRCUIT BREAKER TYPE Julius Sohns,Erlangen, Germany, assignor to Siemens &

Halske Aktiengesellschaft, Berlin and Munich, Germany, a corporation ofGermany Filed Feb. 18, 1963, Ser. No. 259,055

Claims priority, application Germany, Feb. 23, 1962,

3 Claims. (Cl. 317-11) The invention disclosed herein is concerned witha Switch in combination with a thermistor, the resistance of whichincreases with increasing temperature, to decrease the load on contactscontrolled by the switch.

There are switches of the circuit breaker type known, for protecting,for example, lines or motors, which effect in the case of short circuitsor overload a generally magnetically controlled cutout operation. At thecontacts of such switches appears, upon cutout in the presence of ashort circuit, a pronounced contact-frying action which reduces theuseful life of the contacts materially.

The invention is concerned with a switch of the above noted type whereina considerable reduction of the contact frying action is achieved byconnecting the switch in series with a thermistor, the resistance valueof which increases with increasing temperature, practically suddenly,for example, by more than one power of ten, such resistance increaseoccurring within a definite temperature range, which depends upon thecomposition of the thermistor material.

A properly dimensioned thermistor remains cold and has low resistance inthe presence of the rated current on the switch. Upon appearance of ashort circuit or considerable overload, the thermistor will be heated bythe current flowing therethrough, and its resistance will increase. Theshunt or overload current is thereby greatly reduced thus materiallyreducing the load on the contacts.

According to another feature of the invention, the thermistor isstructurally combined with the switch, being disposed, for example, inthe same housing therewith.

The invention will now be explained more in detail with reference to theaccompanying drawing showing in schematic manner an embodiment thereof.

Referring now to the drawing, numerals 1 and 2 indicate terminals of aswitch, for example, a switch of the circuit breaker or cutout type, andnumerals 3 and 4 indicate contacts which are disposed in series with amagnet coil ICC 5 and a thermistor 6. These elements are traversed bythe line current, the coil 5 governing the operation of a magnet whichin turn controls the contacts 3 and 4 to open the circuit when the ratedcurrent is exceeded. The thermistor 6 is dimensioned so that it is onlynegligibly heated and presents low resistance to rated current flowingin the circuit. Upon considerable increase of the current, for example,in the case of a short circuit on the line, the thermistor will beheated and its resistance will suddenly increase in leaping fashion,thus reducing the current flowing through the coil 6 and the contacts 3and 4, without, however, impeding the operative actuation of themagnetic controlled by the coil 5. The frying of the contact-s uponopening thereof is in this manner reduced and the useful life of thecontacts is increased.

Changes may be made within the scope and spirit of the appended claimswhich define What is believed to be new and desired to have protected byLetters Patent.

I claim:

1. A switch of the circuit breaker type having terminals to which isconnected a circuit which is to be supervised, comprising a controldevice connected with said terminals, said control device comprisingmagnetically governed break contacts, means for operatively supportingsaid contacts, a thermistor, and circuit means for serially conmeetingsaid break contacts with said thermistor, said contacts openingresponsive to current flowing in said circuit which exceeds the ratedcurrent flowing therein, to interrupt said circuit, the resistance ofsaid thermistor increasing suddenly in leap-like manner within a giventemperature range, thereby decreasing the current traversing saidcontacts upon breaking action thereof.

2. A switch according to claim 1, wherein said sudden increase ofresistance of said thermistor amounts to more than one power of tens.

3. A switch according to claim 1, wherein said device forms a structuralunit with the switch.

References Cited by the Examiner UNITED STATES PATENTS 1,694,223 12/1928 Lemmon 317-1 1 1,784,226 12/1930 Edsall 317-11 2,594,890 4/1952Ellwood 31711 FOREIGN PATENTS 415,083 10/ 1962 Germany.

SAMUEL BERNSTEIN, Primary Examiner.

1. A SWITCH OF THE CIRCUIT BREAKER TYPE HAVING TERMINALS TO WHICH ISCONNECTED A CIRCUIT WHICH IS TO BE SUPERVISED, COMPRISING A CONTROLDEVICE CONNECTED WITH SAID TERMINALS, SAID CONTROL DEVICE COMPRISINGMAGNETICALLY GOVERNED BREAK CONTACTS, MEANS FOR OPERATIVELY SUPPORTINGSAID CONTACTS, A THERMISTOR, AND CIRCUIT MEANS FOR SERIALLY CONNECTINGSAID BREAK CONTACTS WITH SAID THERMISTOR, SAID CONTACTS OPENINGRESPONSIVE TO CURRENT FLOWING IN SAID CIRCUIT WHICH EXCEEDS THE RATEDCURRENT FLOWING THEREIN, TO INTERRUPT SAID CIRCUIT, THE RESISTANCE OFSAID THERMISTOR INCREASING SUDDENLY IN LEAP-LIKE MANNER WITHIN A GIVENTEMPERATURE RANGE, THEREBY DECREASING THE CURRENT TRAVERSING SAIDCONTACTS UPON BREAKING ACTION THEREOF.